Bearings are a critical component in all HVAC equipment. Bearing life is usually expressed as the number of hours an individual bearing will operate before the first evidence of metal fatigue develops. The usual life rating for industrial applications is called “L-10” life. Simply put the L-10 life is the number of hours in service that 90% of bearings will survive. Or, conversely, 10% of bearings will have failed in the L-10 number of service hours.
L10 life: is the preferred term in specifying bearing life and is defined by The American Bearing Manufacturers Association (ABMA).
L50 or average life: is accepted as the bearing life associated with a 50% reliability, i.e., after a stated amount of time, only 50% of a group of identical bearings will not yet have developed metal fatigue.
L50 life equals five times the L10 life. The following chart shows a comparison of L10 to L50 equivalents.
|Required L10 – Life Hours||Equivalent L50 (avg) Life Hours|
The bearing life rating is theoretical and based on statistics. Specifying a L10 life does not guarantee that the bearings will have a 90% reliability when installed in real world applications. The calculation for Basic Rating Life assumes proper lubrication, no shock or vibration, perfect alignment, debris free environment and temperatures that are not extreme. In the real world, none of these conditions are realistic and the “installed life” of the bearing will depend on the application and maintenance.
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